The fastest moving manmade object on Earth is believed to be a steel manhole cover launched during the 1957 Pascal-B nuclear test, part of the U.S. Operation Plumbbob series conducted at the Nevada Test Site (NTS). The NTS is a 1,350-square-mile reservation located about 65 miles northwest of Las Vegas, Nevada, established in 1951 as the primary continental U.S. site for nuclear weapons testing[1][2][4].
To be more accurate, the steel plate launched in the Plumbbob Pascal-B test was not an actual manhole cover. It weighed about 900 kilograms (2,000 pounds) and was roughly 4 feet (about 1.2 meters) in diameter, making it significantly larger and nearly four to ten times heavier than a standard cast iron manhole cover, which typically weighs between 90 and 250 pounds (40 to 115 kilograms) and measures about 24 inches (0.6 meters) in diameter.
Context of Operation Plumbbob
Operation Plumbbob was the sixth major nuclear test series at the Nevada Test Site, running from May 28 to October 7, 1957. It consisted of 29 nuclear detonations designed to test weapon designs, safety features, and gather data for military and civilian applications. The series included atmospheric, tower, balloon, underground shaft, and tunnel tests, making it the largest and longest test series conducted in Nevada at that time[3][4][6][7].
How the Atomic Bomb Launched the Manhole Cover Without Vaporizing It
During the Pascal-B test, a 300-ton-yield nuclear device was detonated at the bottom of a roughly 500-foot-deep, 4-foot-diameter vertical shaft sealed at the surface by a heavy steel cap weighing about 900 kilograms (2,000 pounds), resembling a manhole cover. Just above the bomb was a 2-ton concrete plug.
When the bomb detonated, it vaporized the concrete plug, creating an extremely high-pressure, superheated gas. This expanding gas acted like the propellant in a giant gun barrel formed by the shaft, propelling the steel cap upward at extraordinary velocity. Because the cap was located far enough from the bomb’s core, it avoided immediate vaporization by the extreme heat and radiation of the explosion. Instead, it was accelerated by the gas pressure generated from the vaporized concrete plug, allowing it to remain mostly intact during launch[7].
A high-speed camera captured the steel cap in only one frame due to its incredible speed. From this, scientists estimated its velocity at about 66 km/s (41 miles per second)—roughly six times Earth’s escape velocity of approximately 11 km/s. This speed would have been sufficient for the cap to leave Earth’s gravitational field.
Debate on Atmospheric Survival and Where the Manhole Cover May Be Now
There is ongoing debate about whether the steel cap survived its passage through Earth’s atmosphere. Many experts argue it would have vaporized due to intense frictional heating, as it lacked any heat shielding. However, some physics simulations suggest parts of it could have survived to exit the atmosphere. If so, the cap may now be traveling through interplanetary space, possibly beyond Pluto’s orbit, making it one of the few manmade objects to have escaped Earth entirely—though it remains lost and untracked[7].
What did the steel cap look like?
There are no known publicly available photographs showing the steel cap (often called a “manhole cover”) from Operation Plumbbob’s Pascal-B test before it was launched, but detailed descriptions and some diagrams exist. While official test photos from Operation Plumbbob exist, none clearly depict the steel cap in place atop the shaft immediately before detonation. The high-speed camera footage captured the cap only in a single frame as it was launched at extreme velocity, but this footage is not publicly available. Most historical records rely on technical descriptions and eyewitness accounts rather than photographic evidence of the cap before launch.
Before it was launched in the Pascal-B test, the steel cap was a solid, round steel plate about 4 feet (1.2 meters) in diameter and 4 inches thick, weighing roughly 900 kilograms (2,000 pounds). It was welded to the top of the 4-foot diameter test shaft at the Nevada Test Site to seal the shaft and was unpainted, plain heavy steel with a flat, disk-like shape similar to a large manhole cover but much thicker and heavier. The cap was designed to withstand handling and sealing the shaft rather than for any aerodynamic purpose.
Comparison to Voyager Spacecraft and the Parker Solar Probe
The Pascal-B manhole cover holds the record for the highest initial velocity achieved by a manmade object launched from Earth, though it was an uncontrolled, accidental event.
– Voyager 1, launched in 1977, is currently the fastest human-made spacecraft traveling through interstellar space at about 17 km/s (38,000 mph) relative to the Sun. Its launch speed relative to Earth was approximately 16.6 km/s (37,000 mph), significantly slower than the Pascal-B manhole cover’s initial velocity but representing a controlled, sustained speed as it journeys beyond the solar system.
– The Parker Solar Probe, launched in 2018, is the fastest human-made object relative to the Sun, reaching speeds up to about 191 km/s (430,000 mph) at perihelion in late 2024. Its speed relative to Earth at perihelion varies between approximately 150 km/s and 220 km/s (335,000 to 490,000 mph), depending on Earth’s orbital position. The Parker Probe’s launch speed from Earth was around 9.2 km/s (20,600 mph), boosted by its Delta IV Heavy launch vehicle and Venus gravity assists to achieve its record-breaking speeds near the Sun[7].
Summary
– The Pascal-B nuclear test at the Nevada Test Site’s Operation Plumbbob launched a 900-kg steel cap at an estimated 66 km/s by vaporizing a concrete plug, which generated a superheated gas that propelled the cap like a projectile through the test shaft.
– Its speed was about six times Earth’s escape velocity, making it the fastest manmade object initially launched from Earth.
– While it likely vaporized in the atmosphere, if it survived, it may now be traveling beyond Pluto’s orbit, lost in interplanetary space.
– Voyager 1 and the Parker Solar Probe are the fastest controlled spacecraft, with Voyager traveling at about 17 km/s relative to the Sun and Parker Solar Probe reaching speeds up to 191 km/s near the Sun. However, their launch speeds from Earth were much lower than the Pascal-B manhole cover’s initial velocity.
This extraordinary event remains a unique example of how nuclear testing at the Nevada Test Site unintentionally created the fastest manmade projectile, predating the space age and conventional rocket launches[1][2][3][4][7].
Read More
[1] https://ahf.nuclearmuseum.org/ahf/location/nevada-test-site/
[2] https://en.wikipedia.org/wiki/Nevada_Test_Site
[3] https://www.llnl.gov/hood-event-plumbbob-operation-nevada-test-site
[4] https://ahf.nuclearmuseum.org/ahf/history/operation-plumbbob-1957/
[5] https://nnss.gov/wp-content/uploads/2023/04/DOENV_715_Rev1.pdf
[6] https://www.wikiwand.com/en/articles/Operation_Plumbbob
[7] https://nuclearweaponarchive.org/Usa/Tests/Plumbob.html
[8] https://virtualglobetrotting.com/map/project-plumbbob-rainier-shot-first-us-underground-nuclear-test/view/google/
[9] https://history.utah.gov/front-row-seat-to-atomic-age/